This invention relates to moisture-reactive hot-melt compositions useful as adhesives, to a method for making such compositions, to a method for bonding substrates with such compositions, and to bonded composite articles made by such a method for bonding.
Some moisture-reactive hot-melt compositions are useful as reactive hot-melt adhesives. Some desirable properties of such adhesives are suitable cure times; high ultimate strength (i.e., high strength after the curing reaction is effectively completed); good adhesion to polyolefins and other substrates to which adhesion is often difficult; and high ultimate strength at elevated temperature (also called “heat resistance”). Some useful reactive hot-melt adhesives are known that contain polyurethane polymers and/or prepolymers.
Hot melt polyurethane compositions may be formulated by the addition of a variety of thermoplastic polymers. With effective choices of thermoplastic polymers, such formulations sometimes have good adhesion to polyolefin substrates, but such formulations are known in the art to lack heat resistance and to require undesirably long times for the curing reaction between the adhesive and moisture to reach completion. U.S. Pat. No. 6,355,317 discloses the use of silicon-containing atmospheric curing resins and the use of isocyanate-functional moisture-curing resins. Many atmospheric curing resins based solely on silicon-type curing reactions are known in the art to require undesirably long cure times. The object of the present invention is the provision of moisture-curable hot melt compositions that reach a useful level of adhesive strength in a usefully short time, that adhere well to polyolefin and other substrates to which it is difficult to adhere, and that reach desirably high levels of heat resistance.